Automatic feedwater control system and method of operating same



March 1965 R. D. HOTTENSTINE 3,175,541

AUTOMATIC FEEDWATER CONTROL SYSTEM AND METHOD OF OPERATING SAME Filed March 25, 196:

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l I I! I 5 3 O 20 25 l 54 26 LOAD 1 22 l HEATING H 2 URFACE 52 I l L20 I ,10 1o SERVO- ECON. I "own 49 z I 52 48 A l\ E I 46 I 46 4s r 3 l l I 1 i l 44 34 4 ,G 1.,(1. 8 e an 42 sP I 42 7 33 32 43 INVENTOR; RICHARD D. HOTTENSTINE ATTORNEY United States Patent 3,175,541 AUTOMATIC FEEDWATER CONTROL SYSTEM AND METHOD OF OPERATING SAME Richard D. Hottenstine, Windsor, Conn., assignor to Combustion Engineering, Inc., Windsor, C0nn., a corporation of Delaware Filed Mar. 25, 1963, Ser. No. 267,507 9 Claims. (Cl. 122-451) This invention relates generally to the control of flow of a vaporizable fluid to a vapor generator. More particularly, it relates to an improved control system for supplying a vapor generator with accurate amounts of feedwater to achieve the desired vapor characteristics over the full range of generator operation and the method of operating the same.

In the past, the need for highly accurate admission of feedwater to vapor generators was not as great as presentday requirements dictate. This was due to the fact that the volume provided in the fluid system by boiler drums provided suificient tolerance to compensate for inaccurate feedwater supply. These errors in feedwater supply appeared in the boiler drum as 2. raising or lowering of boiler water level. But with the advent of massive, high capacity once-through vapor generators and highly automated vapor generators, it has become necessary to control the admission of feedwater to the generators in a highly accurate manner. Such control is necessitated by the fact that the temperature and pressure characteristics of the vapor emerging from such generators is primarily dependent on the rate at which the generator is supplied with feedwater and, in order to closely regulate the characteristics of the vapor created, it is therefore necessary to accurately control the admission of feedwater to the fluid system.

One method of controlling feedwater supply commonly employed in present-day practice involves the use of flow meters which automatically adjust the feedwater supply valve in response to a signal emitted by a load demand sensing device such that an accurate supply of feedwater to the heating surface of the generator is obtained. Such a control system is limited in that conventional flow meters are not accurate over the full load range of high capacity vapor generators to the extent necessary to insure the generation of vapor having close tolerance temperature and pressure characteristics. Plow meters which are accurate within low flow ranges are not accurate within the high flow-high load ranges required by such generators and conversely, flow meters accurate at high flow rates are inaccurate within low flow-low load ranges. To provide flow meters which are accurate within both high and low load-flow ranges is tremendously expensive therefore rendering their use undesirable.

It is a principal object therefore of the present invention to alleviate this problem by providing a feedwater control system that permits the use of conventional, comparatively inexpensive flow meters throughout the entire load range of a vapor generator and therefore materially reduce the cost of obtaining highly accurate feedwater control. The invention contemplates the use of individual flow meters, one of which is accurate for low flow rates and employed when the generator is operating at low loads where the amount of feedwater supplied to the fluid system is low and the other, which is accurate at high flow rates and is employed when the generator is operating at high loads where the amount of feedwater supplied is high. This system is so designed that the ranges of the two flow meters overlap such that the feedwater supply is always under control and the system further provides a means for controlling the operation of the flow meters that permits a smooth operational transition from one flow meter to the 3,175,541 Patented Mar. 30, 19d? other as the load on the vapor generator increases from startup to full operating capacity.

Moreover, the control system is so designed that the flow meter employed at low generator loads can be utilized for metering the flow of operating fluid supplied to desuperheating apparatus where this fluid is obtained from the same source as is the generator feedwater. This additional function for the low flow meter is desirable since it eliminates a period of inoperation for the meter thereby rendering this system more efficient. The added function is permitted due to the fact that desuperheating of vapor is not normally undertaken until the generator load eX- ceeds 25 percent of rated capacity during which time this meter would normally be inoperative, the control of feedwater having been undertaken by the other flow meter in the system.

Accordingly, it is an object of the present invention to provide an improved control organization for supplying vaporizable fluid to a vapor generator.

It is a further object of the present invention to provide a control system for metering the feedwater supply to a vapor generator over its full range of operation in an accurate and inexpensive manner.

Another object of the invention is to provide an improved control system for metering vaporizable fluid to a vapor generator in which one of the flow meters employed for metering feedwater to the vapor generator at low loads can be employed for metering operating fluid to the desuperheater at high generator loads.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

The invention is described with reference to the accompanying drawings wherein:

FIG. 1 is a schematic representation of one form of feedwater control system for a vapor generator contemplated by the instant invention;

FIG. 2 is a graphic representation of the signal response of the flow meters over the generator load range; and

FIG. 3 is a partial schematic representation of a slightly modified form of feedwater control system.

Referring now to the drawings, wherein like characters are used throughout to designate like elements, there is shown in FIGURE 1 a schematic representation of the fluid system 10 of a vapor generator which may be operated at supercritical or subcritical pressures. While the system depicted in the drawing and described herein is of the once-through type, it is to be understood that the present invention is equally adaptable to vapor generators of the recirculation type. As shown, the fluid system comprises a feed pump 12 which forces the vaporizable working fluid or feedwater through a flow measuring device 14 and a flow control valve 16 into the economizer 18. From the economizer 18 the vaporizable working fluid flows through a heating surface 20 and from here through a connecting conduit 22 to the final or finishing heating surface 24. While flowing through the economizer 18 and heating surface 20 the working fluid extracts heat from combustion gases generated in the furnace of the vapor generator by burners (not shown) whereby it is transformed into vapor, either saturated or containing an amount of superheat.

In order to control the characteristics of the vapor emerging from the vapor generator an attemporator or desuperheater 26 is positioned in the connecting conduit 22 to reduce the amount of superheat contained in the vapor leaving the heating surface 20 before it enters the finishing heating surface 24. In the illustrative example the desuperheater 26 is of the spray or direct contact type wherein relatively cool water, which may be obtained from the same source as is the feedwater employed in the generator, is sprayed into the superheated Vapor flowing through the conduit 22. The superheater provides a transient control for the final temperature of the vapor which emerges from the vapor generator.

The vapor, after it leaves the vapor generator at the desired temperature and pressure, is delivered to a vapor operated prime mover which may be a turbine or the like, passing through the valve 28 and then to the prime mover (not shown). The prime mover in conventional systems drives an electricgenerator. As is common in power plant systems, the vapor, upon leaving the prime mover is condensed, heated by suitable preheaters, deaerated and returned to the through-flow circuit, being again forced therethrough by means of the pump 12.

It is well known that the supply of vapor to prime movers from once-through or high capacity recirculating types of vapor generators can be controlled by controlling the amount of feedwater or vaporizable working medium delivered to the fluid circuit. This can be accomplished by changing the setting of the flow control valve 16 or by altering the speed of the feed pump 12 in response to the load demand on the vapor generator. The accuracy of control in such systems is enhanced by adjusting the valve setting or pump speed in response to the amount of fluid flow as determined by a flow measuring device, such as that designated as 14, and which may be any suitable means, such as a venturi meter or flow nozzle. Control is effected by means of a flow transducer which imparts a signal representing the actual flow experienced by the flow measuring device to asurnmation point where it is compared with a desired set point signal corresponding to the load demand on the generator. This comparison provides an error signal if the feedwater flow is not at the desired value and this error signal is transmitted to a controller which adjusts the setting of the flow control valve until the desired rate of flow is obtained.

It can be well understood therefore, that the efficiency of the vapor generator in supplying vapor to the prime mover in varying amounts as the load on the prime mover changes is largely dependent upon the accuracy with which feedwater is supplied to the fluid system which is, in turn, dependent upon the accuracy of the means employed to measure the flow of feedwater through the system over the entire load range of the vapor generator. Conventional vapor generators which employ this type of control have had to rely on the use of a single flow measuring device, such as that shown at '14 over the entire load range of the generator. Because of this fact the flow measuring device was required to be extremely accurate over all ranges of flows which the vapor generator would experience thereby rendering its cost exceedingly expensive.

In accordance with the present invention there is provided a means obviating the need for a single flow measuring means accurate over the entire range of vapor generator operation comprising a bypass line 30 around the flow control valve 16 which contains a bypass flow measuring device 32 and a bypass flow control valve 34. This line comprises part of the vapor generator fluid system and is adapted to conduct feedwater from the feed pump 12 to the economizer 18 when the vapor generator is operating at low loads, for example from O to 25 of rated capacity. The bypass flow measuring device 32, because it is required to measure only low flows, may be a conventional flow measuring device which is accurate over this limited range of flow. Feedwater passes through the bypass line 36 until the vapor generator reaches 25% of its rated capacity when the bypass flow control valve 34 is closed and the main flow control valve 16 is opened.

The control system employed for controlling the flow of fluid through the fluid system comprises flow transducers 36 and 38 which emit signals corresponding to the rates of flow measured by the main flow measuring device 14 and bypass flow measuring device 32. These signals are transmitted through a signal ratioing device comprising contacts 40 and 4t) and an adjustable switch operated by a servo motor 41 to a summation point 42 Where the signal is compared with a desired set point signal designated as 43 corresponding to the load demand on the vapor generator. The set point signal 43 may be derived from any conventional load measuring means, such as means measuring megawatt output of the power plant, outlet pressure of the vapor generator, or the like. This comparison provides an error signal which 1s transmitted to a controller 44, which in turn transm ts the signal to whichever of the flow control valves, 16 or 34, is in operation through a switching device comprising contacts 46 and 46' and an adjustable switching arm operated by a servo motor 48 to adjust the valve being operated to deliver the desired feedwater flow to the vapor generator.

The servo motor 41 is driven in response to the load on the vapor generator as determined by the rate of feedwater flow flowing through the main flow measuring device 14 by means of a controller 56. The arrangement is such that at generator loads of from 0 to 20% the adjustable switching arm of the ratioing device closes contact 40 thereby elfecting control of feedwater flow by means of the signal emitted by the bypass flow measuring device 32 to the bypass flow control Valve 34. When the load on the vapor generator exceeds 20% of rated generator capacity the servo motor 41 is actuated by the controller 50 and the switching arm begins its movement from contact 40 to contact 40' thereby splitting the signal to the summation point 42 and controller 44 thus eifecting adjustment of the bypass flow control valve 34 by means of the signals emitted by both the bypass flow measuring device 32 and the main flow measuring device 14. When the arm reaches contact 40, which occurs when the generator load reaches 25 of rated capacity, servo motor 48 is actuated to move the adjustable switching arm of the switching device from Contact 46 to contact 46 thereby gradually closing the bypass flow control valve 34 and opening the main flow control valve 16 to thus transfer control of feedwater from the former to the latter. At this point, control of feedwater is effected by the main flow control valve 16 solely in response to the signal emitted by the main flow measuring device 14. This transfer is graphically represented in FIGURE 2 where the solid line indicates control of feedwater in response to the signal emitted by the bypass flow measuring device 32 which is accurate at low flow rates and the dotted line indicates control in response to the signal emited by the main flow measuring device 14 which is accurate at high flow rates.

The operation of the system is as follows: When feed water flow to the vapor generator is initiated, as at start up, the adjustable switching arm of the ratioing device is positioned so as to close the contact 413 and that of the switching device is positioned to close the contact 46; therefore main flow control valve 16 is closed and bypass flow control valve 34 is open and control of the latter is efiected by means of the signal emitted by the bypass flow measuring device 32. Feedwater control continues in this way until the load on the vapor generator reaches 20% of its rated capacity at which time servo motor 41 is actuated gradually moving the adjustable switching arm from con= tact 40 to contact 40' thereby transmitting a portion of each of the signals received firom the flow transducer 38 asso= ciated with the bypass flow measuring device 32 and that; received from the transducer 36 associated with the main flow measuring device 14 to the summation point 42 and v controller 44 and thence to the bypass flow control valve 34 through contact 46 of the switching device. When the. load on the vapor generator reaches 25 of rated capacity the adjustable switching arm of the ratioing device is at contact 46, closing the same thereby effecting control of feedwater flow solely by means of the signal transmitted by the flow transducer 36 associated with the main flow measuring device 14. At this point servo motor 48 is actuated to gradually effect movement of the switching arm from contact 46 to contact 46' thereby closing the bypass flow control valve 34 and opening the main flow control valve 16'which now assumes feedwater flow control in response to the signal emitted by the flow transducer 36 associated with the main fiowmeasuring device 14.

Associated with the present control system is a line 52 for delivering working fiuid to the desuperheater 26. This line connects with the bypass line between the bypass flow measuring device 32 and bypass flow control valve 34 to deliver working fluid in the form of generator feedwater to the desuperheater 26 for the purpose of lowering the amount of superheat in the vapor flowing through connection conduit 22. A control valve 54 is positioned in the line 52 for controlling the amount of working fluid delivered to the desuperheater in order to control the temperature of the vapor emerging from the generator in response to a signal emitted from a temperature sensing device 56 positioned at the vapor generator outlet. The means for controlling the amount of working fiuid delivered to the desuperheater 26 comprises a switching device 58, summation points 60 and 62 and three-action type controllers 64 and 66 which serve to transmit a signal to the control valve 54 for adjusting the amount of working fluid delivered to the superheater. At low flows, when the bypass flow control valve 34 is not fully closed and desuperheating does not normally occur, the switch 58 closes contact 68 thereby establishing a signal circuit from the temperature sensing device 56 to the control valve 54. If it is desired to control the superheat temperature of the vapor leaving the primary heating surface at this time desuperheating can occur in response to the signal emitted by the temperature sensing device 56 which is transmitted to a summation point 60 where it is compared with a set point signal indicated as 70, the difference emerging as an error signal transmitted through a controller 64 directly to the control valve 54 which is thereby adjusted to admit the required amount of working fluid to the desuperheater 26 in order to obtain the desired temperature of vapor flowing in connecting conduit 22. At high flows when the bypass flow control valve 34 is fully closed, desuperheat control is efiected in response to the signal emitted by the flow transducer 38 associated with the bypass flow measuring device 32. At this time, the switching device 58 is moved from the contact 68 to the contact 72 and control is maintained by a comparison at the summation point 62 of a set point signal which comprises the error signal transmitted from the summation point 60 through the controller 64 where it is compared with the flow signal transmitted from the flow transducer 38 associated with the bypass flow measuring device 32 and the difference transmitted as an error signal through the controller 66 to control the valve 54. By means of this circuit the bypass flow measuring device 32 and flow transducer 38, during periods when they would normally be inoperative, are made to operate as a portion of the desuperheat control thereby increasing the over-all efiiciency of the control circuit.

FIGURE 3 depicts a slightly modified version of the present invention wherein feedwater control, rather than being effected by adjustment of the main flow control valve 16, is accomplished by varying the speed of the feed pump 12. The system shown in FIGURE 3 is the same as that shown in FIGURE 1 except that the signal transmitted by the controller 44 when the adjustable switching arm of the switching device closes contact 46 is transmited to a means 74 for adjusting the speed of the feed pump 12 rather than to a means for adjusting the setting of the main flow control valve 16.

The control system of the invention, while it has been described herein as being electrical in nature, may be hydraulic or may employ air pressure. An electrical system is preferred because of its convenience and the controllers 44, 64 and 66 indicated may be any of the three-action type, i.e., those providing proportional action, integrating action and differential action, such as the three-action controllers manufactured by Leeds & Northrup Company or the Hagan Company, or the like. The controller indicated at 50 need not provide or use either the ditierential action or the integrating action since such actions are of no particular advantage. The summation points 42, 60 and 62 indicated need no controlling hardware if an electrical system is used since they are merely Wiring points where DC. voltage systems are combined or compared.

It will be understood that various changes in the details, materials, and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. A vapor generator having a feedwater supply system comprising a feedwater inlet line; first flow regulating means for regulating the flow of feedwater through said inlet line; first flow metering means for measuring the flow of feedwater through said inlet line and for emitting a signal in response to said flow; second fiow regulating means, independent of said first flow regulating means, having its outlet connected to said feedwater inlet line downstream of said first flow regulating means; second flow metering means for measuring the flow of fcedwater through said second flow regulating means and for emitting a signal in response to said fiow; vapor generator load sensing means adapted to emit a signal in response to the load demand on said vapor generator; control means including means for actuating each of said flow regulating means in response to said load demand signals and for regulating their operation in response to the signals emitted by said first and second flow metering means, and means for eiiecting regulation of feedwater flow at low flow rates in response to the signal emitted by said second fiow metering means and for transferring regulation of feedwater fiow to the signal emitted by said first flow metering means at high fiow rates.

2. A vapor generator having a feedwater supply sys tem comprising a feedwater inlet line; a first valve interposed in said feedwater valve inlet line for regulating the flow of feedwater therethrough; first flow metering means for measuring the flow of feedwater through said inlet line and for emitting a signal in a response to said flow; a second valve, independent of said first valve, having its outlet connected to said feedwater inlet line downstream of said first valve; second flow metering means for measuring the flow of feedwater through said second valve and for emitting a signal in response to said flow; vapor generator load sensing means adapted to emit a signal in response to the load demand on said vapor generator; control means including means for actuating said valves in response to said load demand signal and for regulating their operation in response to the signal emitted by said first and second flow metering means, and means for efiiecting regulation of feedwater flow at low flow rates in response to the signal emitted by said second flow metering means and for transferring regulation of feedwater flow to the signal emitted by said first flow metering means at high flow rates.

3. A vapor generator feedwater supply system comprising feedwater inlet line; a first valve interposed in said feedwater inlet line for regulating the flow of feedwater therethrough; first fiow metering means accurate over a range of high flow rates for measuring the flow of feedwater through said inlet line and for emitting a signal in response to said flow to regulate the flow to said vapor generator; a second valve, independent of said first valve, having its outlet connected to said feedwater inlet line downstream of said first valve; second flow metering means accurate over a range of loW flow rates for measuring the flow of feedWater through said second valve and for emitting a signal in response to said flow to regulate the flow to said vapor generator; vapor generator load sensing means adapted to emit a signal in response to the load demand on said vapor generator; control means including means for actuating said second valve in response to a low load demand signal and said first valve in response to a high load demand signal and for regulating their operation in response to the signals emitted by said first and second flow metering means, and signal divider means operative to effect regulation of feedwater flow at low flow rates in response to the signal emitted by said second flow metering means and for transferring regulation of feed Water flow to the signal emitted by said first flow metering means at high flow rates.

4. In combination with a vapor generator, a feedwater supply system comprising a feedwater inlet line; a first valve interposed in said feedwater inlet line for regulating the flow of feedwater therethrough; first flow metering means actuate over a range of high flow rates positioned in said feedwater line upstream of said first valve for measuring the flow of feedWater through said inlet line and for emitting a signal in response to said flow to elfect regulation of said flow; a second valve, independent of said first valve, located in bypass relation therewith, and adapted to regulate the flow of feedwater to said vapor generator; second flow metering means accurate over a range of low flow rates for measuring the flow of feed- Water through said second valve and for emitting a signal in response to said flow to effect regulation thereof; vapor generator load sensing means adapted to emit a signal in response to the load demand on said vapor generator; control means including valve actuating means for rendering said second valve operative over low range of load demand in response to said load demand signal and said first valve over a high range of load demand in response to said load demand signal and for regulating their operation in response to the signals emitted by said first and second flow metering means, and signal divider means operative to effect regulation of said second valve solely by the signal emitted by said second flow metering means at low flow rates, by the combined signals of said first and second flow metering means at intermediate flow rates and operative to effect regulation of said first valve solely by the signal emitted by said first flow metering means at high flow rates.

5. A vapor generator including a desuperheater having a feedwater and desuperheater supply system comprising an inlet line; first flow regulating means for regulating the flow through said inlet line; first flow metering means for measuring the fiow through said inlet line and for emitting a signal in response thereto; second flow regulating means, independent of said first flow regulating means, having its outlet connected to said inlet line downstream of said first flow regulating means; second flow metering means for measuring the flow through said secflow regulating means in response to the signal'emitted by said second flow metering means.

6. A method for regulating feedwater flow to a vapor generator having first flow regulator means, second flow regulator means in bypass relation With said first flow regulator means, flow metering means associated with each of said flow regulator means, means for operating said flow regulator means in response to said fiow metering means and means for actuating said fiow regulator means in response to vapor generator load requirements comprising the steps of regulating the admission of feedwater to said vapor generator over a first load range by operating one of said flow regulator means and controlling its operation by its associated fioW metering means; regulating the admission of feedwater to said vapor generator over a second load range by the continued operation of said one flow regulator means but transferring control thereof to both flow metering means; and regulating the admission of feedwater to said vapor generator over a third load range by transferring the operation from said one flow regulator means to the other of said flow regulator means and controlling its operation by its associated flow metering means.

7. A method for regulating feedWater flow to a vapor generator having first flow regulator means, second flow regulator means in bypass relation with said first regulator means, first flow metering means accurate over a range of high vapor generator load requirements associated with said first flow regulator means, second flow metering means accurate over a range of low vapor generator load requirements associated With said second flow regulating means, means for operating said flow regulator means in response to said flow metering means and means for actuating said flow regulator means in response to vapor generator load requirements comprising the steps of regulating the admission of feedwater to said vapor genera-tor over a range of low vapor generator load requirements by operating said second flow regulator means and controlling its operation by said second flow metering means; regulating the admission of feedwater to said vapor generator over a range of intermediate vapor generator load 7 requirements by said second flow regulator means but transferring control of its'operation to both flow metering means; and regulating the admission of feedwater to said vapor generator over a range of high vapor generator load requirements by transferring the operation from said second flow regulator means to said first flow regulator means controlling its operation by said first flow metering means.

8. A method for regulating feedwater flow to a vapor generator having first flow regulator means, second flow regulator means in bypass relation with said first flow regulator means, first signal emitting flow metering means accurate over a range of high vapor generator load requirements associated with said first flow regulator means,

I second signal emitting flow metering means accurate over ond flow means and for emitting a signal in response thereto; third flow regulating means connected in parallel relation with said second flow regulating means for regulating the flow of Water to said desuperheater; vapor generator load sensing means adapted to emit a signal in response to the load demand on said vapor generator; control means including means for actuating said first and second flow regulating means in response to said load demand signals and for regulating their operation in response to the signals emitted by said first and second flow metering means; means for elfecting regulation of feedwater flow at low flow rates in response to the signal emitted by said second flow metering means and for transferring regula- I a range of low vapor generator load requirements associated with said second flow regulator means, signal responsive means to operate said flow regulator means in response to said flow metering means including means associated with said'second flow regulator means for operating the same by the combined operation of both flow metering means and means for actuating said How regulator means in response to vapor generator load requirements comprising the steps of regulating the admission of feedwater to said vapor generator over a range of low vapor generator load requirements by operating said second flow regulator means and controlling its operation by a signal emitted by said second flow meter- 1ng means; regulating the admission of feedwater to said vapor generator over a range of intermediate vapor generator load requirements by the continued operation of said second flow regulator means but transferring the control thereof to the summation of signals of both flow metering means; and regulating the admission of feed- Water to said vapor generator over a range of high vapor generator load requirements by transferring the operation from said second flow regulator means to said first flow regulator means and controlling its operation by a signal emitted by said first flow metering means.

9. A method for regulating feedwater and desuperheater Water flow to a vapor generator having a desuperheater, first flow regulator means, second flow regulator means in bypass relation with said first flow regulator means, third flow regulator means for regulating flow to said desuperheater in parallel with said second flow regulator means, first flow metering means associated with said first flow regulator means, second flow metering means associated with said second and third flow regulator means, means for operating said flow regulator means in response to said flow metering means and means for actuating said flow regulator means in response to vapor generator load requirements comprising the steps of regulating the admission of feedwater to said vapor generator over a range of low vapor generator load requirements by operating said second flow regulator means and controlling its operation by said second flow metering means; regulating the admission of feedwater to said vapor generator over a range of intermediate vapor generator load requirements by the continued operation of said second flow regulator means but transferring the control thereof to both flow metering means; and regulating the admission of feedwater to said vapor generator over a range of high vapor generator load requirements by transferring the operation from said second flow regulator means to said first flow regulator means and controlling its operation by said first flow metering means; while regulating the admission of water flow to said desuperheater over said range of high vapor generator load requirements by said third fiow regulator means and controlling its operation by said second flow metering means.

References Cited by the Examiner UNITED STATES PATENTS 3,096,744 7/63 Profos 122479 FOREIGN PATENTS 884,132 6/61 Great Britain.

OTHER REFERENCES German application Ser. No. E 7776, printed August 30, 1956 (K1. 13g9).

ROBERT A. OLEARY, Primary Examiner.

Examiners. 

1. A VAPOR GENERATOR HAVING A FEEDWATER SUPPLY SYSTEM COMPRISING FEEDWATER INLET LINE; FIRST FLOW REGULATING MEANS FOR REGULATING THE FLOW OF FEEDWATER THROUGH SAID INLET LINE; FIRST FLOW METERING MEANS FOR MEASURING THE FLOW OF FEEDWATER THROUGH SAID INLET LINE AND FOR EMITTING A SIGNAL IN RESPONSE TO SAID FLOW; SECOND FLOW REGULATING MEANS, INDEPENDENT OF SAID FIRST FLOW REGULATING MEANS, HAVING ITS OUTLET CONNECTED TO SAID FEEDWATER INLET LINE DOWNSTREAM OF SAID FIRST FLOW REGULATING MEANS; SECOND FLOW METERING MEANS FOR MEASURING THE FLOW OF FEEDWATER THROUGH SAID SECOND FLOW REGULATING MEANS AND FOR EMITTING A SIGNAL IN RESPONSE TO SAID FLOW; VAPOR GENERATOR LOAD SENSING MEANS ADAPTED TO EMIT A SIGNAL IN RESPONSE TO THE LOAD DEMAND ON SAID VAPOR GENERATOR; CONTROL MEANS INCLUDING MEANS FOR ACTUATING EACH OF SAID FLOW REGULATING MEANS IN RESPONSE TO SAID LOAD DEMAND SIGNALS AND FOR REGULATING THEIR OPERATION IN RESPONSE TO THE SIGNALS EMITTED BY SAID FIRST AND SECOND FLOW METERING MEANS, AND MEANS FOR EFFECTING REGULATION OF FEEDWATER FLOW AT LOW FLOW RATES IN RESPONSE TO THE SIGNAL EMITTED BY SAID SECOND FLOW METERING MEANS AND FOR TRANSFERRING REGULATION OF FEEDWATER FLOW TO THE SIGNAL EMITTED BY SAID FIRST FLOW METERING MEANS AT HIGH FLOW RATES. 